An airbag inflator provides gasses to inflate an airbag to protect a vehicle occupant during a crash. An airbag inflator can be a pyrotechnic inflator employing only a burnable a gas generant or a hybrid inflator employing both a stored inert gas and a burnable gas generant for producing inflation gasses. These two types of inflators are well known in the art and are commonly used in the automotive industry. The requirements for these safety devices have evolved dramatically as the knowledge and science of vehicle crash scenarios has evolved. As a result the need exists for inflators to provide a very reliable and predictable inflation of an airbag that can adjust the impact of the airbag on vehicle occupants.
Airbags must provide protection for a variety of vehicle occupants and seating positions as defined in the Federal regulations. One way to meet this requirement is to provide an airbag inflator that provides a range of inflation gas output. Currently this is most often satisfied using a dual stage inflator that provides both a low and high gas output. The low output condition is used for out of position and small stature vehicle occupants while the higher output is used for properly positioned and large stature vehicle occupants. An ideal inflator would be able to provide for both conditions with a single stage. To accomplish this goal the initial performance must match the low output performance for the first part of the deployment and then accelerate the output to achieve the higher output. The ideal inflator would use only one deployment signal and would require no additional input from the electronic control unit. This type of gas output is typically described as an “S-Curve”.
In prior art airbag inflators this S-Curve performance is simulated by the use of two igniters that are typically activated sequentially causing an initial burning of a portion of a gas generant within an inflator and thereafter the second igniter is activated causing a second portion of the gas generant to be ignited. This enables the airbag to initiate deployment with a less aggressive or softer impact on the vehicle occupant and then to increase the cushioning forces to provide maximum protection.
The complexity of the timing and use of two separate igniters adds to the concern of component failure or malfunction. Almost all of these low to high output inflators require the use of two separate igniters activated sequentially by separate signals.
The present invention can provide the desired low to high gas output without using two igniters. The invention provides a reliable and extremely predictable delay in the combustion of the internally held gas generant material within the inflator housing of either a pyrotechnic or a hybrid inflator.